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Date: Fri, 27 Dec 2019 16:20:11 +0000
From: Michael =?utf-8?B?S2rDtnJsaW5n?= <michael@kjorling.se>
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Subject: Re: [dm-crypt] How to compress LUKS2 header?
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To: dm-crypt@saout.de

On 27 Dec 2019 10:56 -0500, from gebser@mousecar.com (ken):
> Compressing a file is one step in the encryption of that file.  So if
> your LUKS2 header file is encrypted, it's also already compressed. 
> Using ZIP on it would yield no further compression.

No, encryption does not imply compression. Rather, trying to compress
ciphertext is a largely pointless exercise if the encryption is any
good in the first place; therefore, _if_ you're going to compress the
data you're encrypting (keeping in mind that doing so is not always a
good idea; see compression oracle attacks), then you need to compress
first, then encrypt, not the other way around.

I'm pretty sure the LUKS header backup isn't compressed.

-- 
Michael Kjörling • https://michael.kjorling.se • michael@kjorling.se
 “Remember when, on the Internet, nobody cared that you were a dog?”